The field of the invention is adhesion promoters.
In many composite materials, and particularly in composite materials that include rubber and polymeric fibers, adhesion between the polymeric fibers and the rubber is a significant factor in the overall performance of such composite materials, and numerous approaches are known in the art to improve adhesion between a polymeric fiber and a rubber composition.
In one approach, the surface of a polymeric fiber is physically modified with an electron beam to create particular chemically reactive groups that are then involved in forming covalent bonds between the polymeric fiber and the rubber as described in U.S. Pat. No. 4,794,041 to Gillberg-LaForce et al. Treating polyethylene terephthalate (PET) materials with an e-beam advantageously generates reactive groups (e.g., carboxylate or hydroxyl groups) on the PET surface, which may react with epoxy or isocyanate groups in the adhesive coating on the polymeric fiber to improve bonding between the PET material and a rubber. However, e-beam treatment tends to increase production cost. Moreover, Gillberg-LaForce""s approach typically requires installation of relatively large and energy consuming equipment.
In another approach, the surface is chemically modified with a solvent to improve adhesion of a rubber composition of the fiber as described, for example, in U.S. Pat. No. 3,644,136 to McCullough et al or U.S. Pat. No. 3,902,950 to Tung et al. Surface treatment of a polymeric fiber is relatively simple, and may even be performed in some cases without specialized equipment. However, the use of halo-organic solvents in such treatments frequently poses environmental and/or health concerns. Moreover, surface treatment with halo-organic solvents typically still necessitates in many cases the use of resorcinol-formaldehyde-latex (RFL) to improve rubber adhesion.
To circumvent at least some of the problems associated with surface treatments, polymeric fibers may be covered with an additional layer. Such layers may be applied in the form of a spin finish, overfinish, or by dipping the polymeric fiber into one or more adhesives. There are numerous examples known in the art, and exemplary methods and compositions for spin-finish coating are described in U.S. Pat. No. 4,467,064 to Kudo et al. or U.S. Pat. No. 4,477,497 to Kudo et al. Exemplary methods and compositions for over-finish coating are described in JP 8,246,353 to Kitahara et al., and exemplary methods and compositions for dip coating are described in U.S. Pat. No. 3,429,354 to Malcom or U.S. Pat. No. 3,903,332 to Kelly et al. Although providing additional layers onto the surface of polymeric fibers frequently improves the adhesion of rubber to the fibers, the additional layers generally still need an RFL adhesive coating, which is environmentally problematic and may pose significant heath threats to workers exposed to resorcinol and formaldehyde.
In still other approaches, RFL is replaced with an acrylic resin with a molecular weight of between about 100,000 and 1,000,000 that is mixed with resorcinol-formaldehyde free latex as described by Solomon et al. in U.S. Pat. No. 4,472,463. While the use of Solomon""s resins allows omission of RFL and tends to improve adhesion of latex to a substrate, the use of such resins typically requires a two-step dip process (e.g., a polyepoxide dip and an acrylic-rubber latex mixture). Moreover, Solomon""s resins lack crosslinking functionalities to the latex, thereby potentially reducing optimal adhesion.
Alternatively, maleinized polybutadiene may be employed to eliminate the use of RFL as described in a paper presented at the 155th Rubber Division of the ACS, Chicago, Ill., Apr. 13-16, 1999 (xe2x80x9cMaleinized Polybutadiene Latex for Fiber to Rubberxe2x80x9d by A. S. Estrin and R. W. Nalepa). Although such compositions may advantageously replace RFL in some instances, maleinized polybutadiene has relatively poor water solubility and generally requires the use of sodium, potassium or ammonium hydroxides for formation of lattices and solutions in water. Moreover, adhesion of such compositions to fibers is at least in some cases less than desirable.
Although various methods and compositions for improving adhesion between a polymeric fiber and rubber are known in the art, all or almost all of them suffer from one or more disadvantages. Thus, there is still a need to provide compositions and methods for improved adhesion promoters.
The present invention is directed to an adhesion promoter comprising a polymeric strand with an epoxy-reactive group other than a phenolic hydroxyl group and a crosslinking group, wherein the crosslinking group is capable of crosslinking the polymeric strand with a rubber in a crosslinking reaction, and wherein the polymeric strand is water soluble in an amount of no less than 10 g/l, and more preferably no less than 100 g/l.
In one aspect of the inventive subject matter, the polymeric strand comprises an organic polymer, preferably polybutadiene, and more preferably a polybutadiene that is maleinized and wherein at least one carboxyl group of the maleic acid is esterified with methoxy polyethylene glycol. Especially contemplated epoxy-reactive groups include carboxylic acid groups, and especially contemplated crosslinking groups comprise a double bond which may or may not be located within the backbone of the polymeric strand. Consequently, the crosslinking reaction may involve a covalent bond with a sulfur atom, or a nucleophilic/electrophilic addition, or a cyclo-addition.
In another aspect of the inventive subject matter, contemplated adhesion promoters further comprise a second polymer, preferably a styrene-butadiene-vinylpyridine copolymer (e.g., styrene-butadiene-vinylpyridine latex). Contemplated rubbers include synthetic and natural rubbers, and it is especially preferred that the rubber may further comprise polybutadiene grafted with maleic anhydride, or that the rubber may further comprise hexamethylene tetramine, resorcinol and silica.
In a further aspect of the inventive subject matter, a rubber containing product comprises a polymeric fiber coated with a compound having a plurality of epoxy groups, wherein the polymeric fiber is coupled to a rubber via an adhesion promoter. Contemplated adhesion promoters preferably comprise a polymeric strand with an epoxy-reactive group other than a phenolic hydroxyl group, and further comprise a crosslinking group that crosslinks the polymeric strand with the rubber, and have a water solubility of no less than 10 g/l, and more preferably no less than 100 g/l. Contemplated adhesion promoters may further comprise a second polymer, preferably a styrene-butadiene-vinylpyridine copolymer (e.g., styrene-butadiene-vinylpyridine latex).
In a still further aspect of the inventive subject matter, a method of fabricating a rubber-containing product comprises a step in which rubber, and a polymeric fiber comprising a plurality of epoxy groups are provided. In a further step, an adhesion promoter is provided having a polymeric strand with an epoxy-reactive group other than a phenolic hydroxyl group, and further having a crosslinking group, and wherein the adhesion promoter is water soluble in an amount of no less than 10 g/l, and more preferably no less than 100 g/l, and in a still further step the rubber is covalently coupled with the polymeric fiber via the adhesion promoter, wherein the epoxy-reactive group forms a covalent bond with the epoxy group, and wherein the crosslinking group forms another covalent bond with the rubber. Contemplated adhesion promoters may further comprise a second polymer, preferably a styrene-butadiene-vinylpyridine copolymer (e.g., styrene-butadiene-vinylpyridine latex).
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawing.